I think it's mostly that I am baffled at the idea of measuring butter in 'cups'. Because, no. I'm prepared to look up (yet again, as it is information that refuses to stay in my head) the size of a 'stick' of American butter (ours are bigger), because that is a sensible way to measure the stuff. Otherwise, butter must be weighed!

I do have a set of measuring cups, and for sugar, or water, etc, this system perfectly sensible. (Though see hsw's comment above re measuring flour in cups - that's a lot of trouble to go to!) But to be asked to add 3/4 cup of butter makes no sense to me. :-)